Boundaries

The base of the pyramidally shaped PPS sits at the skull base and is defined by the spine of the sphenoid bone laterally, insertion of the pharyngobasilar fascia to the petrous portion of the temporal bone medially, the scaphoid fossa anteriorly, and the posterior aspect of the jugular foramen posteriorly. The apex forms at the greater cornu of the hyoid bone. The lateral boundary of the PPS is defined by the medial pterygoid muscle and fascia, and this separates the PPS from the masticator space and infratemporal fossa. ^, The medial boundary is formed by the pharyngobasilar fascia. The posterior boundary is formed by the prevertebral fascia. The anatomical boundaries of the PPS are depicted, Figure 1 .

Lateral view of the parapharyngeal space and surrounding structures underneath the mandible (outlined in dotted white). Outlined, the parapharyngeal space (purple) and styloid diaphragm (green).

Base of skull surgical landmarks

At the base of the pyramid, there are 3 important bony structures and 3 fascial attachments which define important landmarks with surgical relevance. Anteriorly, the space is bound by the apex of the scaphoid fossa. Proximal to the lateral margin of the scaphoid fossa, the medial pterygoid muscle attaches, continuing posteriorly where it extends medial to the foramen ovale and foramen spinosum to its attachment site on the spine of the sphenoid bone. At the most posterolateral end of the space lies the styloid process. Medially, the jugular foramen transmits the internal jugular vein (IJV) and cranial nerves IX, X, and XI. Medial to this, the hypoglossal canal transmits CN XII. Anteriorly, the carotid canal transmits the internal carotid artery (ICA).

Jugular foramen

The jugular foramen is located on the posterior aspect of the petrooccipital fissure, between the petrosal part of the temporal bone and the condylar part of the occipital bone. Several structures traverse the foramen, including the sigmoid sinus and jugular bulb, cranial nerves IX through XI and their ganglia. The dura on the intracranial surface of the foramen contains two perforations by which nerves are transmitted. The smaller anteromedial perforation, the glossopharyngeal meatus, transmits CN IX. The larger posterolateral perforation, the vagal meatus, transmits CN X and XI. In one study of 10 cadavers, these were separated by a fibrous septum in 80% of specimens (20 hemi-heads). Within the foramen, the superior jugular bulb is separated from CNs IX, X, and XI via a sheet of loose connective tissue. The right foramen is notably larger than the left but large levels of variability is the rule rather than the exception. ^, On average, its diameter is about 8.5mm, but its size is largely variable. Radiographically the jugular foramen is commonly described in two parts, separated by a fibrous septum or the jugular spine, pars nervosa: anteromedial and smaller and pars vascularis: posterolateral and larger. Both contain cranial nerves and vessels.

Hypoglossal canal

The hypoglossal canal lies at the base of skull near the occipital condyles. Described as oval in shape, it extends from the posterior fossa to the nasopharyngeal carotid space. The jugular foramen can be found laterally, and the occipital condyle found posteromedially, with the external orifice of the hypoglossal canal situated above the anterior third of the condyle. ^{, ,} The hypoglossal canal transmits CN IX, the meningeal branch of the ascending pharyngeal artery (APA), and a venous plexus. ^, It is oriented anterolateral to the occipital condyles; with occasional observance of an external bony spine or septal partition, however, it typically does not have either. ^, In a study of 50 adult skulls, no significant difference between left and right canals were identified, with a mean length of 8.46 mm and external diameter of 6.38 mm. Similar measurements have been noted throughout the literature. ^,

Tensor-vascular-styloid fascia

The Tensor-vascular-styloid fascia (TVSF), also known as styloid diaphragm, is a fibrous sheet of connective tissue continuous with the anterior carotid sheath, Figure 2 . It originates at the styloid process where it attaches laterally and superiorly to the anterior surface of the vaginal process just posterior to the sphenoid spine. It extends to the inferior border of the tensor veli palatini muscle posterolaterally. It then fuses with a mesh network of fascial layers contributing to the anterior carotid sheath. During its course, it covers the styloid apparatus laterally. It ultimately divides the PPS into two compartments: an anterolateral pre styloid space and a posteromedial post styloid space, Figure 3 .

Division of the prestyloid and poststyloid space by the styloid diaphragm. Parapharyngeal space is outlined in dotted black line and styloid diaphragm is outlined in green.

Pre styloid and post styloid space divided by the TVSF. Parapharyngeal space is indicated by the dashed line. Carotid space is demarcated by the dotted line. Parotid gland (PG), masseter (M), temporalis (T), medial pterygoid (MP), tensor veli palantini (TVP), internal carotid artery (ICA), CN X (X), internal jugular vein (IJV), sphenoid process (SP).

Styloid muscles

The styloid process of the petrous temporal bone serves as a distinct landmark within the PPS. It serves as the origin for the styloid muscles, the stylohyoid, stylopharyngeus and styloglossus as well as the stylohyoid and stylomandibular ligaments. Together, these muscles help facilitate movement of the tongue, pharynx, larynx, hyoid and mandible. The stylohyoid muscle is a small thin muscle that originates from the posterior surface of the styloid process near its base. It travels anteroinferiorly and medially to insert into the tissue aponeurosis near the lesser cornu of the hyoid. The stylohyoid ligament arises at the distal tip of the styloid process and inserts at the lesser cornu of the hyoid bone. Anteromedial to the stylohyoid muscle, the styloglossus muscle arises at the anterior border of the styloid process coursing with the stylohyoid and inserting above the lesser cornu of the hyoid bone. On the medial surface of the styloid process arises the stylopharyngeus muscle. It runs anteroinferiorly towards the lateral side of the pharynx.

Pre styloid space

The pre styloid space lies anterolateral to the TVSF. It is a fat filled compartment bordered by the medial pterygoid laterally and superior constrictor muscle medially. The masticator and parotid spaces are located laterally, while the pharyngeal mucosal sits medial. It contains a portion of the deep lobe of the parotid gland, APA, the pharyngeal vein, the pterygoid venous plexus, lymph nodes, minor salivary glands, and the mandibular nerve.

The deep lobe of the parotid

The parotid gland lies lateral to the PPS and is enclosed in a layer of deep cervical fascia, often called the parotid fascia. The facial nerve divides the gland into two lobes, superficial and deep, described in Peraza et al. The majority of the deep lobe lies deep to the facial nerve but lateral to the ramus of the mandible. The retromandibular component extends towards the PPS. It is separated from the PPS by the stylomandibular ligament, a thickened portion of the parotid fascia attached to both the styloid process and the angle of the mandible. This creates a space between the parotid gland and the PPS, termed the stylomandibular tunnel. The stylomandibular tunnel is located between the ramus of the mandible anteriorly and the stylomandibular ligament posteriorly. The deep lobe of the parotid gland, more specifically the retromandibular portion, will occasionally extend through the stylomandibular tunnel and into the pre styloid PPS. Therefore, changes in the size of the tunnel noted on serial imaging are often indicative of a PPS tumor. When the stylomandibular tunnel widens over time, this indicates there is a mass originating from the parotid gland, due to space constrictions with the parotid space. In contrast, a narrowed stylomandibular tunnel suggests a mass arising in the post styloid space. A mass in the retromandibular portion of the deep lobe will displace the parapharyngeal fat medially which is a clue on diagnostic CT that a mass is coming from the parotid space and not the other surrounding tissues.

Ascending pharyngeal artery (APA)

The APA arises from the external carotid artery (ECA) proximal to the bifurcation of the common carotid artery. ^, It arises from the medial surface of the ECA, ^, but has also been described to arise from the posterior aspect of the ECA in almost equal frequency. ^, Rarely, it is said to arise from the occipital artery, carotid bifurcation, or ICA. Though it commonly only arises as one root, a second accessory APA has been observed. ^, Its origin is often described as “high” or distal to the lingual artery. ^, It ascends posteromedial to the ICA, coursing along the anterior surface of the longus capitis muscle within the PPS. ^, The artery branches into two major trunks: anteriorly, the pharyngeal trunk, which supplies the pharynx, and posteriorly, the neuromeningeal trunk, which enters the intracranial space through foramen magnum.

Pterygoid venous plexus

The pterygoid venous plexus lies between the temporalis and lateral pterygoid muscles, and partly between the lateral and medial pterygoid muscles. It serves as a site for venous anastomosis in the space between the sphenomandibular ligament and the neck of the mandible. It provides venous drainage from the nasal cavity, paranasal sinuses, and nasopharynx into the maxillary vein and has been described in detail previously. The pterygoid venous plexus can serve as a site of copious venous bleeding during manipulation of tumors within the PPS.

Mandibular nerve

The mandibular nerve has been previously described in detail. In short, it exits the skull base through the foramen ovale on the lateral aspect of the PPS. It then courses inferomedially to the otic ganglion which lies within the infratemporal fossa. After dividing into an anterior and posterior trunk, it gives rise to several nerves, including the deep temporal, mesenteric, and lateral pterygoid nerves from its anterior trunk and the buccal, lingual, inferior alveolar nerve (IAN) and auriculotemporal nerve (ATN) from its posterior trunk.

Post styloid space

The post styloid space, often termed the carotid space or retro styloid space, refers to the posteromedial portion of the PPS in relation to the TVSF. Within it lies the ICA, IJV, the initial extracranial segment of cranial nerves IX, X, XI and XII, and the sympathetic trunk.

Internal carotid artery (ICA)

The ICA arises as a branch of the common carotid trunk at the level of C3-C4. It ascends cranially, coursing posteriorly to the ECA but anteromedially to the IJV. Throughout the PPS, it is found within the carotid sheath. From an endoscopic ventral view, via the nasal or oral cavity approach, it can be observed posterior to the lateral portion of the cartilaginous part of the eustachian tube. ^, It is also observed posterior to the levator veli palatini muscle, and posterolateral to the deepest aspect of the fossa of Rosenmüller. It is located between the levator veli palatini muscle and stylopharyngeus muscle in the upper PPS. It continues its course to the external orifice of the carotid canal. Nair et al. assessed the distance between the ICA and several surgical landmarks at the level of C1-C2 interspace among 30 CT-Angiograms (60 sides) and 8 cadaveric heads (16 sides). Across the cadaveric study they noted the mean distance of the ICA to the fossa of Rosenmüller was 8.5 ± 1.4 mm. The distance to torus tubarius was 19.8 ± 1.3 mm and to the medial and lateral pterygoid plates were 25.3 ± 1.4 mm and 18.2 ± 1.4 mm, respectively. These measurements were accurate within 1 mm distance in the radiographic findings. Notably, they identified the fossa of Rosenmüller as the closest neighboring structure to the ICA, serving as an important surgical landmark. Within the PPS, the ICA can be identified as medial and posterior to the posterior trunk of V3, which runs a relatively parallel course.

Internal jugular vein (IJV)

The IJV is continuous with the sigmoid sinus. At the base of skull, the sinus drains into the superior jugular bulb, which lies posteriorly within the jugular foramen. Its dome is variable in shape and size but is typically described as rounded or conical. The IJV then exits the foramen from the posterior aspect and descends vertically within the PPS. Within the post styloid PPS, the IJV lies lateral to the ICA. It typically exhibits a diameter of 6.2 mm on average, with the right IJV being larger than the left most commonly but is highly variable. As it descends, it can be identified at the posteromedial aspect of the styloid process, although occasionally observed posterolaterally. It reaches the posterior side of the sternal end of the clavicle where it merges with the subclavian vein to form the brachiocephalic vein.

Glossopharyngeal nerve (CN IX)

The glossopharyngeal nerve provides motor and sensory information to the oral cavity and pharynx, secretomotor fibers for the parotid, taste fibers for the posterior 1/3 of the tongue, and motor fibers for the stylopharyngeus. It originates at the medulla oblongata and emerges from the cerebellomedullary cistern immediately below the bulbopontine sulcus and directly above the origin of the rostral rootlets of the vagus nerve. ^, It consists of a larger dorsal root and frequently a small ventral root. Its fibers course anteriorly and laterally along the jugular tubercle of the occipital bone towards the jugular foramen at the skull base. It enters the anteromedial perforation of the dura where it meets the vagus and accessory nerves. ^{, , ,} It exits near the top of the jugular foramen through the intrajugular part. ^, It courses anteriorly through the foramen, with a slight lateral obliquity. Here, it gives off the tympanic nerve from its inferior ganglion. Upon exiting the jugular foramen, it continues to descend, traveling medial to the jugular vein and posterior to the ICA within the carotid sheath. Upon reaching C1, it begins to travel on the lateral surface of the carotid artery, descending posterior to the styloid process. It travels posterior to the stylopharyngeus muscle, providing motor innervation to the muscle and other structures. ^, Just below the foramen ovale, the glossopharyngeal nerve fibers leave the otic ganglion to merge with the ATN, a branch of the trigeminal nerve. The nerve then continues its course posteriorly in the PPS to surround the middle meningeal artery, crossing along the medial edge of the condylar apophysis of the mandible and entering the parotid gland. CN IX gives off the carotid sinus and carotid body nerve, also named Hering’s Nerve. It enters the pharynx between the upper and middle constrictor muscles at the posterior border of the hyoglossus muscle at the point where the stylopharyngeus muscle merges with the constrictors. ^, It provides sensory innervation to the posterior third of the tongue and motor innervation to the stylopharyngeus muscle.

Vagus nerve (CN X)

The vagus nerve is primarily responsible for providing parasympathetic activity, but also contains sensory and brachial motor fibers. A range of rootlets (4-15 rootlets) originating at the medulla oblongata, inferior to CN IX, come together at the jugular foramen to form the vagus nerve. As they descend, they are largely indistinguishable from fibers of CN XI. They enter the dura via the posterolateral perforation where they are met by CN XI. As the vagus nerve exits via the jugular foramen it gives rise to the inferior and superior ganglions. The superior ganglion is typically appreciated within the jugular foramen whereas the inferior ganglion is typically located below the extracranial orifice of the jugular foramen, typically at level C2. The fibers of CN X remain in intimate proximity to CN XI, and both CNs X and XI maintain a posterior orientation to CN IX. ^, The inferior ganglion gives rise to several branches in communication with CN IX and CN XI. ^, At the inferior aspect of the inferior ganglion, the pharyngeal nerve arises. This nerve ascends anteriorly, joining with a branch from the glossopharyngeal nerve. At the same level of the inferior ganglion, the superior laryngeal nerve (SLN) arises, branching into internal and external branches deep to the carotid bifurcation, at the level of C3. ^, After branching, the internal branch of the SLN travels medially and anteriorly piercing the thyrohyoid membrane to provide sensory innervation to the mucosa of the larynx above the vocal cords. The external branch of the SLN descends along the lateral aspect of the larynx, parallel to the superior thyroid artery and innervating the cricothyroid muscle. The main trunk of the CN X travels inferiorly, enclosed within the carotid sheath. Here, it courses posterolaterally to the internal and common carotid arteries, and medially to the IJV. ^,

Spinal accessory nerve (CN XI)

The spinal accessory nerve is often described as two distinct segments which ultimately innervate the sternocleidomastoid and trapezius. The spinal portion arises from the upper five or six rootlets of cervical levels C1 to C5 while the cervical portion arises from four or five rootlets of the medulla oblongata. ^, Spinal rootlets enter the posterior cranial fossa through the foramen magnum before merging with the cranial roots to form the common trunk. The nerve exits the skull base through the jugular foramen, lateral to the vagus nerve, but anterior or anteromedial to the IJV. At the level of the posterior belly of the digastric muscle, CN XI is generally found superficial and lateral to the IJV, but its location can vary greatly. CN XI has also been observed to cross posterior to the IJV as it courses to the jugular foramen. ^, Several fibers of CN XI connect with the superior ganglion of the vagus nerve. This typically occurs at the level of the upper border of the transverse process of the atlas. The main trunk of CN XI travels lateral to the IJV and enters the post styloid space. Here it separates into cervical and spinal roots, in which the cervical roots join CN X, and the spinal roots continue lateral to the IJV and medial to the styloid process. ^, Notably, one study including 56 cadavers (112 sides) found that in 88% of specimens, the spinal accessory nerve travels anterior to the IJV within the post styloid space. In a separate study of 30 cadavers (60 sides) this was also true in 71.7% of specimens.

Hypoglossal nerve (CN XII)

The hypoglossal nerve arises as several rootlets at the posterior aspect of the medulla oblongata. Within the premedullary cistern it is described to course anterolaterally, between the posterior inferior cerebellar artery (PICA) and the vertebral artery. The nerve was noted to be posterior to the vertebral artery in 93% of cases in a cadaveric study of 10 specimens. It passes through the anteromedial perforation of the dura and into the hypoglossal canal. Within the hypoglossal canal, it is enclosed within arachnoid, dural sheath and a venous plexus. This plexus is only noted within the canal. CN XII exits at the inferolateral part of the canal, adjacent to where CN X emerges from the jugular foramen. Upon exiting the hypoglossal canal, it joins CN IX and X, coursing in a bundle within the carotid sheath. ^{, ,} CN XII is described to initially course anterior to both CN IX and X. At the level of the inferior ganglion of CN X, it crosses posteriorly, giving rise to several fibers in direct communication with the ganglion. ^, CN XII then descends in between the ICA and IJV until it reaches the transverse process of the atlas where it takes a sharp turn along the anterior surface of the ICA, crossing to the lateral side of the ECA. ^, The level in which this cross occurs is highly variable. It continues between the greater horn of the hyoid bone and middle tendon of the digastric muscle towards the inferior surface of the tongue where it innervates all intrinsic and extrinsic tongue musculature, except for the palatoglossus which is innervated by CN X. The transverse process of the atlas (C1) also serves as an important surgical landmark in lateral neck dissections. Here, the occipital branch of the occipital artery which runs lateral to C1, becomes tethered inferiorly to this bony landmark and is easily identifiable during surgical interventions.

Sympathetic trunk

The cervical sympathetic trunk (CST) begins at the skull base, traveling along the lateral sides of the vertebral column bilaterally. It serves to distribute sympathetic neurons and postganglionic fibers throughout the body. The cervical sympathetic trunk consists of a main trunk with several ganglia: the superior ganglion, middle ganglion, inferior ganglion, cervicothoracic ganglion, and vertebral ganglion. The number of ganglia present varies by individual but in a study of 24 CSTs, 45.8% of the specimens had only two ganglia present, typically the superior and the cervicothoracic ganglia or the superior and inferior ganglia. Classically, the CST is described as having 3 ganglia present. Notably, in this study, the superior ganglia was observed in all specimens. Most commonly, specimens had superior and cervicothoracic ganglia. The superior ganglion is typically located at the level of the C2-3 transverse process. It lies posterior to the ICA and sheath and anterior to the longus capitis. ^, When present the middle ganglion was present between C5-7 while the inferior ganglion was noted at C7-T1. The vertebral ganglion was less common but described to be anteromedial to the vertebral artery by Kiray et al., and the vertebral nerve described to be posterior to the vertebral artery by Saylam et al. The cervicothoracic ganglion is formed by the merging of the inferior and first thoracic sympathetic ganglion, with its upper pole arising at the level of the C7 transverse process and medial to the vertebral artery. ^, The CST is located anterior to the anterior tubercle of the transverse process with anterior vertebral musculature separating the two. It almost always passes over the longus colli muscle, though it is important to recognize possible variants in its precise location relative to the longus colli to avoid injury during surgery. ^, At the level of C6 where the transverse process lies, the CST is roughly 2.2 and 2.8 mm in diameter, serving as an important surgical landmark during anterior or anterolateral approaches.

Lymph nodes

Located medially to the ICA, the retropharyngeal lymph nodes, otherwise known as Rouvière nodes, provide draining from the nasopharynx, paranasal sinuses, soft palate, pharynx, middle ears and eustachian tubes. They drain into the deep jugular chain and the upper spinal accessory nodes. These nodes are frequently described as two groups; medial and lateral. The medial retropharyngeal nodes lie directly posterior to the pharynx, at the level of C2 and are often inconstant in number and location, typically only one is found if at all. They are often small in size, with an average thickness of 0.8 mm, and often absent, with one study reporting medial retropharyngeal nodes in only one of eleven specimens. The lateral nodes can be found near the lateral aspect of the pharynx overlying the longus capitis and longus coli muscles. Specifically, they have been identified to be located at the apex of the PPS. They are constant in size, averaging about 7.2 × 3.8 × 2 mm in one study of eleven cadavers. While more common than the medial retropharyngeal nodes, they were observed in only 55% of specimens. When observed, they range from 1 to 3 nodes and vertically aligned with one another when multiples were found.

Tumor heterogeneity

Fewer than 0.5% of head and neck neoplasms originate in the PPS. The most common neoplasm of this space is the benign mixed tumor, or pleomorphic adenoma, which most often arises from extension of the parotid gland but can also arise from ectopic salivary gland tissue in the PPS. ^, Paragangliomas are the second most common tumor of the PPS. There have been limited reports of benign lipomas, second branchial cleft cysts or vascular malformations in this space, and other types of malignant lesions such as liposarcoma or osteosarcoma, both of which are extremely rare. Metastatic tumors can spread to the PPS, most often from the thyroid gland. Approximately 80% of tumors found in the PPS are benign and 20% are malignant.

Pre styloid space tumors

We have defined the pre styloid space as the portion of the PPS anterolateral to the TVSF which contains the retromandibular portion of the deep lobe of the parotid gland. Therefore, almost all tumors which are found in the pre styloid space are of parotid origin, with the most common of these being pleomorphic adenomas. Malignant tumors which can be found in this space include malignant salivary neoplasms such as mucoepidermoid carcinoma, adenoid cystic carcinoma, acinic cell carcinoma, and many others. Deep lobe parotid tumors can extend into the stylomandibular tunnel, creating a dumbbell shape as the tumor becomes wedged between the skull base superiorly and posteriorly, the ramus of the mandible anteriorly and the stylomandibular ligament inferiorly as it spans from the parotid space into the pre styloid space. Radiographically it is important to look at the displacement of the pre styloid parapharyngeal fat as it often indicates the space in which the tumor originated in narrowing the differential diagnosis.

Diagnosis

As the retromandibular portion of deep lobe parotid tumors extend into the pre styloid space, masses can grow to a substantial size before becoming symptomatic. Due to this, the most common presentation of patients with a pre styloid space tumor is by incidental finding on imaging. If pre styloid compartment tumors do cause symptoms in patients, these typically are in the form of globus sensation or fullness in the oropharynx, and rarely with pain or cranial nerve deficit. Biopsy of the mass may be performed by ultrasound guided or CT guided fine needle aspiration with core biopsy. In some cases, biopsy is not possible due to the difficult location of the mass. In these cases, or when the tumor is benign appearing on imaging, surgeons may opt to proceed to surgery without biopsy. Although the specific risk of transoral biopsy is not well documented, precautions should be taken before performing a biopsy given an increased risk of tumor spillage and mucosal adherence in deep parotid tumors involving the PPS.

Treatment

Surgical removal is typically recommended to treat tumors in the pre styloid space, whether benign or malignant in nature. When approaching deep lobe parotid tumors which involve the pre styloid space, several approaches can be used based on the location, size, and pathology of the tumor. This space is commonly accessed through a transcervicoparotid approach. Thorough division of the stylomandibular ligament is necessary to remove dumbbell shaped deep lobe parotid tumors extending into the pre styloid space through the stylomandibular tunnel. This is divided with sharp dissection and this maneuver frees the tumor from being wedged against the mandible, allowing blunt dissection of the tumor to continue into the pre styloid space for en bloc removal. Care is taken to avoid tumor capsule disruption, particularly in the case of pleomorphic adenomas which can have an increased risk of tumor recurrence with violation of the capsule. Additional exposure maneuvers for large tumors include subluxing the jaw forward, disrupting the styloid process, or removing a portion of the mastoid tip. Surgeons may choose to nasotracheally intubate to allow anterior displacement of the mandible, and may use temporary internal maxillary fixation to advance the mandible during the case.

During dissection of the tumor, fracturing the styloid process, or even removing it, is a useful maneuver to improve access and facilitate en bloc removal, although the surgeon must be careful not to disrupt the capsule of the tumor on the fractured styloid edge. It is important to fracture the styloid process inferiorly to avoid disrupting the tumor capsule or injuring a vessel. Benign tumors within this space are dissected away from surrounding structures with blunt dissection, typically with a finger sweep. Once a benign tumor is mobilized and pedicled on the deep lobe of the parotid, the pedicle can be clamped, ligated, and sharply divided. In some cases of benign tumors, the tumor involves the majority of the deep lobe of the parotid and extends to abut the facial nerve. In these cases, careful dissection must be performed to identify and preserve the facial nerve branches to avoid permanent facial paralysis. A combined transcervical and transparotid approach should be pursued in these cases. With dissection and manipulation of the facial nerve for tumor removal, temporary facial paresis post operatively is common, but if nerve branches are preserved, facial function tends to return to normal within one year post surgery. ^, . Additional post operative complications associated with parotidectomy such as Frey’s syndrome, first bite syndrome, or sialocele may be experienced by patients undergoing transparotid approach. ^,

Post styloid space tumors

The post styloid space has been defined as the posteromedial portion of the PPS in relation to the TVSF. Tumors may arise from the structures housed within this space and are therefore typically either neurogenic or vascular, the most common types being benign schwannomas and paragangliomas, respectively. Other neurogenic benign or malignant tumors in this space are quite rare.

Diagnosis

Like pre styloid space tumors, masses within the post styloid space are typically noted as an incidental finding on imaging. Post styloid space masses can otherwise present in a variety of ways, most commonly as a palpable neck mass, globus sensation, or swelling of the oropharynx, and less commonly with dysphagia, pain, symptoms of catecholamine excess, Horner syndrome, or cranial nerve deficit. It is important to recognize which structure the tumor is arising from—carotid artery, jugular vein, vagal nerve, sympathetic chain, or other lower cranial nerves—on imaging based on displacement of structures in the post styloid space for patient counseling and surgical planning.

When present in the PPS, carotid body tumors typically displace the ICA medially and the IJV laterally, whereas glomus jugulare tumors displace both the carotid artery and jugular vein medially If the tumor originates from the vagus nerve, the tumor typically displaces the ICA and the ECA anteromedially and the IJV posterolaterally. If the tumor originates from the lower cranial nerves, it will typically displace the carotid vessels posterolaterally. Lastly, if the tumor originates from the sympathetic chain, the carotid sheath will typically be displaced anterolaterally.

Computed tomography angiography (CTA) is often useful for diagnostic purposes, balloon occlusion testing and preoperative embolization for carotid body tumors. The classification system by Furukawa et al. can be used to help distinguish between a schwannoma originating from the vagal nerve vs the sympathetic chain. Saito et al. published a series of 12 patients with PPS schwannomas and found that 80% of sympathetic chain schwannomas and 100% of vagal schwannomas were correctly identified based on the Furukawa criteria. DOTATATE positron emission tomography (PET) scan is often performed to investigate a diagnosis of paraganglioma for the primary tumor as well as look for neuroendocrine tumors elsewhere in the body, and metanephrine/catecholamine lab testing is done to rule out presence of a secreting tumor.

Treatment

Surgical removal is the standard treatment for benign and malignant tumors of the post styloid PPS. However, benign tumors may initially be observed with serial imaging, and in some cases, tumors may be treated with radiation therapy as primary or adjuvant treatment. For benign neurogenic tumors arising from the vagal nerve, for instance, there is a risk of vagal nerve paralysis with surgical enucleation, and complete resection results in vagal paralysis. Therefore, these tumors may be closely monitored, and surgical intervention reserved until after the tumor demonstrates significant growth and/or vocal fold hypo- or immobility is noted. Similarly, after resection of sympathetic chain tumor, patients typically will develop Horner’s syndrome if this was not already present preoperatively. Vascular tumors such as paragangliomas can be treated by resection or irradiation. Sometimes a period of observation is indicated, as these tumors are often slow growing. With vascular tumors, angiography can be helpful in tumor treatment planning, and the surgeon should be prepared to perform vascular repair if necessary.

PPS infections

Infections of the PPS may arise from upper respiratory tract infections/tonsillopharyngitis or direct extension of disease, such as a peritonsillar abscess. Because the PPS abuts several deep neck spaces, it can facilitate the spread of infection to the carotid sheath, retropharynx, submandibular and sublingual, parotid, as well as masticator spaces, and beyond. The buccopharyngeal gap—space between middle and superior pharyngeal constrictors – provides a pathway for infections to spread between the submandibular space and the PPS. The prevertebral fascia which serves as the posterior aspect of the PPS allows for communication with the retropharyngeal space.

Patients with PPS infections may present with signs of systemic infection including fevers and chills. Pre styloid compartment infections, typically preceded by pharyngitis or tonsillitis, may cause dysphagia, trismus and pain of the neck and jaw, as well as otalgia. The neck near the angle of the mandible may exhibit swelling and induration, and on transoral exam there may be bulging of the lateral pharyngeal wall. Post styloid compartment infections may present with sepsis without a clear source on physical examination, frequently necessitating imaging such as a CT scan for diagnosis. Serious complications from PPS infections typically are due to involvement of the post styloid compartment, which contains several vital structures. These may include Horner’s syndrome, lower cranial nerve palsies, suppurative jugular thrombophlebitis (Lemierre syndrome), or carotid artery blowout. Typical treatment regimen includes intravenous antibiotics with or without surgical incision and drainage.